I always try to have two back up journals selected prior to submitting my work to a journal.
First, in case my review is taking too long, or the editor is non-responsive to my queries, I can submit to another journal immediately (after I send a note, of course, withdrawing the article from review). Second, if I get reviews back that are negative, not helpful, or rejections, I have two places in mind already where I can send them to. Not having these in mind can slow you down. Third, by having to select two additional journals, it forces you to assess the nature of these journals for subsequent publications. This can also stimulate new ideas for articles and increase your professional knowledge.